This invention relates to therapeutic agents and peptides, radiotherapeutic agents and peptides, radiodiagnostic agents and peptides, and methods for producing such labeled radiodiagnostic and radiotherapeutic agents. Specifically, the invention relates to cyclic peptide derivatives and analogues of somatostatin, and embodiments of such peptides labeled with gamma-radiation emitting isotopes such as technetium-99m (Tc-99m), as well as methods and kits for making, radiolabeling and using such peptides to image sites in a mammalian body. The invention also relates to peptide derivatives and analogues of somatostatin labeled with cytotoxic radioisotopes such as rhenium-186 (.sup.186 Re) and rhenium-188 (.sup.188 Re), and methods and kits for making, radiolabeling and using such peptides therapeutically in a mammalian body.
Somatostatin is a tetradecapeptide that is endogenously produced by the hypothalamus and pancreas in humans and other mammals. The peptide has the formula: ##STR1##
[Single letter abbreviations for arnino acids can be found in G. Zubay, Biochemistry (2d ed.), 1988, (MacMillan Publishing: New York), p.33]. This peptide exerts a wide variety of biological effects in vivo. It is known to act physiologically on the central nervous system, the hypothalamus, the pancreas, and the gastrointestinal tract.
Somatostatin inhibits the release of insulin and glucagon from the pancreas, inhibits growth hormone release from the hypothalamus, and reduces gastric secretions. Thus, somatostatin has clinical and therapeutic applications for the alleviation of a number of ailments and diseases, both in humans and other animals. Native somatostatin is of limited utility, however, due to its short half-life in vivo, where it is rapidly degraded by peptidases. For this reason, somatostatin analogues having improved in vivo stability have been developed in the prior art.
Freidinger, U.S. Pat. No. 4,235,886 disclose cyclic hexapeptide somatostatin analogues useful in the treatment of a number of diseases in humans.
Coy and Murphy, U.S. Pat. No. 4,485,101 disclose synthetic dodecapeptide somatostatin analogues.
Freidinger, U.S. Pat. No. 4,611,054 disclose cyclic hexapeptide somatostatin analogues useful in the treatment of a number of diseases in humans.
Nutt, U.S. Pat. No. 4,612,366 disclose cyclic hexapeptide somatostatin analogues useful in the treatment of a number of diseases in humans.
Coy et al., U.S. Pat. No. 4,853,371 disclose synthetic octapeptide somatostatin analogues.
Coy and Murphy, U.S. Pat. No. 4,871,717 disclose synthetic heptapeptide somatostatin analogues.
Coy et al., U.S. Pat. No. 4,904,642 disclose synthetic octapeptide somatostatin analogues.
Taylor et al., U.S. Pat. No. 5,073,541 disclose a method of treating small cell lung cancer.
Brady, European Patent Application No. 83111747.8 discloses dicyclic hexapeptide somatostatin analogues useful in the treatment of a number of human diseases.
Bauer et al., European Patent Application No. 85810617.2 disclose somatostatin derivatives useful in the treatment of a number of human diseases.
Eck and Moreau, European Patent Application No. 90302760.5 disclose therapeutic octapeptide somatostatin analogues.
Coy and Murphy, International Patent Application Serial No. PCT/US90107074 disclose somatostatin analogues for therapeutic uses.
Schally et al., European Patent Application Serial No. EPA 911048445.2 disclose cyclic peptides for therapeutic use.
Bodgen and Moreau, International Patent Application Serial No. PCT/US92/01027 disclose compositions and methods for treating proliferative skin disease.
Somatostatin exerts its effects by binding to specific receptors expressed at the cell surface of cells comprising the central nervous system, the hypothalamus, the pancreas, and the gastrointestinal tract. These high-affinity somatostatin binding sites have been found to be abundantly expressed at the cell surface of most endocrine-active tumors arising from these tissues. Expression of high-affinity binding sites for somatostatin is a marker for these tumor cells, and specific binding with somatostatin can be exploited to locate and identify tumor cells in vivo.
Methods for radiolabeling somatostatin analogues that have been modified so as to contain a tyrosine amino acid (Tyr or Y) are known in the prior art.
Albert et al., UK Patent Application 8927255.3 disclose radioimaging using somatostatin derivatives such as octreotide labeled with .sup.123 I.
Bakker et al., 1990, J. Nucl. Med. 31: 1501-1509 describe radioactive iodination of a somatostatin analog and its usefulness in detecting tumors in vivo.
Bakker et al., 1991, J. Nucl. Med. 32: 1184-1189 teach the usefulness of radiolabeled somatostatin for radioimaging in vivo.
Bomanji et al., 1992, J. Nucl. Med. 33: 1121-1124 describe the use of iodinated (Tyr-3) octreotide for imaging metastatic carcinoid tumors.
Alternatively, methods for radiolabeling somatostatin by covalently modifying the peptide to contain a radionuclide-chelating group have been disclosed in the prior art.
Albert et al., UK Patent Application 8927255.3 disclose radioimaging using somatostatin derivatives such as octreotide labeled with .sup.111 In via a chelating group bound to the amino-terminus.
Albert et al., European Patent Application No. WO 91/01144 disclose radioimaging using radiolabeled peptides related to growth factors, hormones, interferons and cytokines and comprised of a specific recognition peptide covalently linked to a radionuclide chelating group.
Albert et al., European Patent Application No. 92810381.1 disclose somatostatin peptides having amino-terminally linked chelators.
Faglia et al., 1991, J. Clin. Endocrinol. Metab. 73: 850-856 describe the detection of somatostatin receptors in patients.
Kwekkeboom et al., 1991, J. Nucl. Med. 32: 981 Abstract #305 relates to radiolabeling somatostatin analogues with .sup.111 In.
Albert et al., 1991, Abstract LM10, 12th American Peptide Symposium: 1991 describe uses for .sup.111 In-labeled diethylene-triaminopentaacetic acid-derivatized somatostatin analogues.
Krenning et al., 1992, J. Nucl. Med. 33: 652-658 describe clinical scintigraphy using [.sup.111 In][DTPA]octreotide.
These methods can be readily adapted to enable detection of tumor cells in vivo by radioimaging, based on the expression of high affinity binding sites for somatostatin on tumor cells. Radionuclides which emit gamma radiation can be readily detected by scintigraphy after injection into a human or an animal. A variety of radionuclides are known to be useful for radioimaging, including .sup.67 Ga, .sup.68 Ga, .sup.99m Tc (Tc-99m), .sup.111 In, .sup.123 I or .sup.125 I. The sensitivity of imaging methods using radioactively-labeled peptides is much higher than other techniques known in the art, since the specific binding of the radioactive peptide concentrates the radioactive signal over the cells of interest, for example, tumor cells. This is particularly important for endocrine-active gastrointestinal tumors, which are usually small, slow-growing and difficult to detect by conventional methods. Labeling with technetium-99m (Tc-99m) is advantageous because the nuclear and radioactive properties of this isotope make it an ideal scintigraphic imaging agent. Tc-.sup.99 m has a single photon energy of 140 keV and a radioactive half-life of about 6 hours, and is readily available from a .sup.99 Mo-.sup.99m Tc generator. Other radionuclides have effective half-lives which are much longer (for example, .sup.111 In, which has a half-life of 60-70 h) or are toxic (for example, if .sup.125 I). Although Tc-99m is an ideal radiolabeling reagent, it has not been widely used in the art prior to the present invention [see, for example, Lamberts, J. Nucl. Med. 32: 1189-1191 (1991)].
Somatostatin and radiolabeled somatostatin analogues can also be used therapeutically. For these applications, cytotoxic radioisotopes are advantageous, such as scandium-47, copper-67, gallium-72, yttrium-90, iodine-125, iodine-131, samarium-153, gadolinium-159, dysprosium-165, holmium-166, ytterbium-175, lutetium-177, rhenium-186, rhenium-188, astatine-211 and bismuth-212. The rhenium isotopes .sup.186 Re and .sup.188 Re are particularly advantageous.
The use of chelating agents for radiolabeling proteins are known in the prior art, and methods for labeling peptides Tc-99m are disclosed in commonly assigned U.S. Pat. Nos. 5,811,394; 5,225,180; 5,443,815; 5,711,931; 5,780,007; 5,849,260; 5,508,020; 5,405,597; 5,225,525; 5,645,815; and 5,561,220 and in allowed U.S. patent application Ser. No. 08/361,864; and in International Applications PCT/US92/00757, PCT/US92/10716, PCT/US93/02320, PCT/US93/03687, PCT/US93/04794, PCT/US93/05372, and PCT/US93/06029, which are hereby incorporated by reference.
Fritzberg, U.S. Pat. No. 4,444,690 describes a series of technetium-chelating agents based on 2,3-bis(mercaptoacetamido) propanoate.
Gansow et al., U.S. Pat. No. 4,472,509 teach methods of manufacturing and purifying Tc-99m chelate-conjugated monoclonal antibodies.
Reno and Bottino, European Patent Application 87300426.1 disclose radiolabeling antibodies with Tc-99m.
Pak et al., European Patent Application No. WO 88/07382 disclose a method for labeling antibodies with Tc-99m.
Cox, International Patent Application No. PCT/US92/04559 discloses radiolabeled somatostatin derivatives containing two cysteine residues.
Rhodes, 1974, Sem. Nucl. Med. 4: 281-293 teach the labeling of human serum albumin with technetium-99m.
Khaw et al., 1982, J. Nucl. Med. 23: 1011-1019 disclose methods for labeling biologically active macromolecules with Tc-99m.
Byrne and Tolman, supra, disclose a bifunctional thiolactone chelating agent for coupling Tc-99m to biological molecules.
Cox et al., 1991, Abstract, 7th International Symposium on Radiopharmacology, p. 16, disclose the use of, Tc-99m-, .sup.131 I- and .sup.111 In-labeled somatostatin analogues in radiolocalization of endocrine tumors in vivo by scintigraphy.
Methods for directly labeling somatostatin, derivatives of somatostatin, analogues of somatostatin or peptides that bind to the somatostatin receptor and contain at least two cysteine residues that form a disulfide or wherein the disulfide is reduced to the sulfhydryl form, are disclosed in U.S. Pat. No. 5,225,180.
There remains a need for synthetic (to make routine manufacture practicable and to ease regulatory acceptance) somatostatin analogues having increased in vivo stability, to be used therapeutically, as scintigraphic agents when radiolabeled with Tc-99m or other detectable radioisotopes for use in imaging tumors in vivo, and as radiotherapeutic agents when radiolabeled with a cytotoxic radioisotope such as rhenium-188. Small synthetic somatostatin analogues are provided by this invention that specifically fulfill this need.